Adjustable cam mechanism



July 5, 1949.

ca. F. DALY ADJUSTABLE CAM MECHANISM 8 Sheets-Sheet 1 Filed Dec. 6, 1944 INVENTOR 650905 /7 0A4 ATTORNEY y 1949- G. F. DALY 2,475,311

I ADJUSTABLE CAM MECHANISM Filed Dec. 6, 1944 8 Sheets-Sheet 2 ATTORNEY July 5, 1949. G. F. DALY 2,475,311

ADJUSTABLE CAM MECHANISM Filed Dec. 6, 1944 8 Sheets-Sheet 5 ATTORNEY G. F. DALY ADJUSTABLE CAM MECHANISM July 5, 1949.

Filed Dec.

8 Sheets-Sheet 4 INVENTOR 650/ 05 DALY ATTORN EY 1949- G. F. DALY 2,475,311

ADJUSTABLE CAM MECHANISM Filed Dec. 6, 1944 8 Sheets-Sheet 5 INVENTOR 050905 /-T DALY ATTORNEY July 5, 1949- GJF. DALY 5 2,475,311

' ADJUSTABLE CAM MECHANISM Filed Dec. 6, 1944 8 Sheets-Sheet 6 INVENTOR (250/205 flALY ATTORNEY July 5, 1949. G; F. DALY ADJUSTABLE CAM MECHANISM 8 Sheets-Sheet 7 Filed Dec. 6, 1944 lNVENTOR 050205 E 0AA) BY WW? ATTORNEY July 5, 1949. I GQF. DALY 2,475,311

ADJUSTABLE CAM MECHANI SM Filed Dec. 6, 1944 a Sheets-Sheet 8 INVENTOR GEORGE E OALY mzm ATTORNEY Patented July 5, 1949 UNITED STATES PATENT OFFICE ADJUSTABLE CAM MECHANISM George F. Daly, Endicott, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application December ,6, 1944, Serial No. 566,804

1 Claim. 1

The present invention relates to an altimeter drum and drive mechanism therefor designed for use in connection with training apparatus of the type shown and described in a publication of August, 1944, entitled Operation, Service and Overhaul Manual, Device 'l-A-S, Horizontal Bombing and Dead Reckoning Trainer, Volume I of two volumes, published under the joint authority of the Commanding General, Army Air Forces, the Chief of the Bureau of Aeronautics and the Air Council of the United Kingdom. A copy of this publication exists in the files of the United States Patent Office.

Briefly, by means of such a training apparatus, a student bombardier is confronted with conditions that closely simulate those which occur during actual flying and which are intended to produce proficiency in the art of bombing. The particular apparatus with which the present invention is associated is in the form of a bombing and dead reckoning trainer which has been designed to duplicate to the utmost degree th flight of an airplane on an actual bombing mission, while at the same time enabling the instructor to observe the bombardiers reactions and give him valuable advice as to his procedure. The apparatus includes, among other things, a bombardiers station wherein the bombardier, in position with his instruments, may view an image of a realistic target which appears to move toward him at a uniform velocity. This target is in the form of a motion picture projected from an overhead projection apparatus onto a screen below the bombardier so that during a bombing run in the trainer the bombardier may take the necessary sights, make the necessary calculations of altitude and airspeed, manipulate his instruments, etc., and otherwise perform all the necessary duties that would be required of him during an actual bombing run.

The invention is primarily concerned with an instructors control station and equipment therefor wherein the instructor is provided with the necessary instruments for setting up bombing problems, together with means for checking the actions of the bombardier.

Still more specifically, the present invention relates to an altimeter drum assembly and drive unit therefor which are enclosed together with other equipment in the instructors instrument panel casing. By means of this equipment, true altitude and average temperature readings which the student bombardier is required to make is made available to the instructor automatically. Briefly, the altimeter drum and drive mechanism therefor comprises a panel proper behind which a drum unit including an altimeter drum per se, is mounted for rotation about a horizontal axis, Surrounding the drum and concentric therewith is a drum shutter mounted for independent turning movement about the common axis of the drum. Printed or otherwise marked on the surface of the drum are certain visible indicia representing indicated altitude and certain other indicia representing true altitude. The readings afforded by these indicia are visible through an elongated horizontally extending window or slot provided in the outer instructor's instrument panel. The various indicia are arranged in circumferential bands or columns around the surface of the drum, one column pertaining to indicated altitude readings and the remaining columns pertaining to true altitude readings.

The drum shutter is provided with an elongated opening through which the indicated altitude readings are visible, while a straight reference line is provided for selecting these readings. The true altimeter readings are selectively visible through the various windows, the latter being arranged at spaced oifset points along the shutter.

Available temperature readings are provided by means of indicating marks on a scale extending alongside the drum and shutter and these latter readings are adapted to be selected by virtue of the positional relationship of the various openings in the shutter which come into alignment with the slot in the in-structors panel as the drum and drum shutter are moved relative to each other.

From the above description it will be seen that indicated altitude readings are a direct function of the position of the drum at any particular instant, while true altitude readings are a combined function of the position of the drum and of the shutter relative to the latter. Average temperature readings are a function of the position of the shutter relative to the slot or window provided in the instrument panel. The altitude drum is adapted to be driven in either direction at a predetermined rate of speed by mean-s of an electric motor. Rotation of the drum in one direction is representative of the climb operation, while rotation thereof in the opposite direction is representative of a dive operation. Reset means are provided for restoring the drum to its initial or zero indication.

Th position of the drum shutter is adapted to be varied by means of a cam cluster slidably mounted or keyed to a cam shaft. The cam shaft is coupled in direct. driving relationship to the shaft upon which the drum is mounted. The cam cluster is adapted to be shifted to bring a selected cam thereof into register with the cam follower and the latter is mechanically connected to the drum shutter in such a manner that as the drum and cams rotate the cam follower causes the position of th shutter to be varied. I I

Each cam in the cluster represents a particular problem requiring different calculations on the part of the student bombardier d ue to temperature variations. The result of'these' 'calculations are made immediately, available .to the instructor and this is made' possiblebythe expedient of altering the position of the drum shutter under the control of theparticular cam which has been selected for operation; The true altitude reading is thus made available to the instructor and at any particular instant true altitude, will be represented, by the particular poj lsition ofth'ej drum and a particular position of :Ithe shutter. The average temperature readings are available to 'the"instructor on the average fte'mperaturefscaleand is a function solely of'the position of the shutter, v v I i Otherobjects of'the invention will be pointed out in the following description and claim and illustrated in'thefaccompanying' drawings, which disclose, Y by way Moi example, the principle of 'the invention and 'the'best mode, which has been jjcont'emplated, of applying'that principle.

In the drawings; t Fig. lisjaperspec'tive view of an instructors Lst'ation including the instructors instrument .panel comprising the present invention.

Fig. 2 is an enlarged perspective view of the "iiistructors instrument'panel assembly with the panel coveri removed to more clearly illustrate the nature of the invention.

Fig. 3 is a side elevationarview of an altimeter drum employed in connection with the present invention.

;,;f Fig. 4 is amend iew of the altimeter drum.

Fig. 5 is a'fragmentary perspective view of an altimeter drive unit'employed in connection {with the present invention.

j'jFiggs is another perspective view of the aljtimeter drive'unit'taken'from a diiferent angle.

Fig. 7 is still another perspective view of the altimeter drive unit,1certain parts] being broken -Y'away to more clearly reveal the nature of the invention.

Fig. 8 is an end view o f the altimeterdrive unit.

Referring nowto Fig. 1, the instructor's in- 7 strument panel is located at a central position on the instructors desk 36 and consists of three major assemblies, namely, an operating" instrument panel 10, analtimeterdrum unit 12' and an altimeter drivev unit 14 (see particularly Fig.

1 2). The instrument panel has associated'therewith a conventional clock or tim piece I6 which has no internal mechanism. or electrical connections and which is secured to an' instrument panel cover 38.

A true airspeed indicator 80, which is designed l to indicate the true airspeed asit exists atthe projector of the trainer under the 'co'ntrol of the instructor, is mounted on the panel cover 38 at the right of theclock 16.

,An indicated airspeed instrument 82; also j' mounted on the cover 38, is provided in order that f v the instructor may" instantaneously determine the airspeed that wouldbejread. on the bombar- "diers "airspeed" indicator iiith'e trainer at the altitude and temperature of the particular problem under consideration. A compass 84, which is mounted on the panel cover at the right of the instructors true airspeed indicator 80, indicates to the instructor the airplane heading.

A drift meter 98 on the panel cover 38 indicate-s to the, instructor the angular relation of the image to the bombardiers compartment in the trainer. A temperature meter I00 of conventional design, and which may be a central reading voltmeter, is also mounted on the panel cover 38 and is provided for the purpose of giving the instructor the temperature reading at any altitude in accordance with certain cam selec- 'tions of which he is capable of making and the nature of which will be described presently.

Referring now to Figs. 1, 3 and 4, at the lefthand side of the panel cover 38 is an opening or window I04 through which there is visible an altimeter drum per se I06 (Fig. 2 which is associated with the drum unit assembly 12. The drum I 06 is mounted on a horizontal shaft I08 (Fig. 3) which issupported in bearings III) and "H2 carried in a pair of side plates H4 and I I6 that project upwardly from and are secured as at I I8 to a pair of cross members I20. The drum proper consists of a cylindrical sheet of parchment or other similar material (Fig. 4) which is mounted on a plurality of spiders'l24 which are 'two coupling members I26, I28 are provided "with a centering pin and hole arrangement I21.

A pair of arms I30 which are secured as at I32 to the side plates II4'and II6 project upwardly at. the sides of the drum I 06 and serve to support therebetween a pair of tightly stretched parallel indicating wires I33 which serve as a reference line for reading two sets of figures or indicia IA and TA respectively, the former meaning indicated altitude and the lattermeaning true altitude. The indicia IA are arranged in an extreme left-hand band or zone extending around the surface of the cylindrical drum, while the indicia TA are arranged in a plurality of similar columns "existing in the medial gitudinal regionsand also at the eXtremeright-hand end of the drum.

A drum shutter lt (Figs. 3 and 4) of substan- 'tiall'y semi-cylindrical design, and which is posi- Ytioned in close proximity to the drum proper I06,

is swingably supportedbetween a' pair of spiders I36, which are mounted on sleeves I40 for free turningmovement on the shaft I08. The shutter I34 is provided with an elongated opening I42 adjacent its left-hand end, as viewed in Fig. 3, through which the indicia IA representing indicated altitude are visible'when these latter indicia are aligned with thewindow I00 formed inthe panel cover 38. The shutter I34 is also provided with a series of diagonally or helically arranged windows I44 of a number equal to'the number of ftruealtitude columns on the drum and each of which is aligned for'movement in register with a respective true altitude 'column. Atth'is point it mayjbe stated that the altitude drum is adapted to be driven ata predetermined rateof speed by means of a motor M (Fig. 2) associated with the altimeter drive unit 14 operating through the internal drive mec ia'n mi'or theunit'in a manner that will appeaipr'e'seniiyh 'Tlie"drum may be I varied at the will of the instructor.

"driven for a gradual climb or a gradual dive under the control of a pair of switches C and D respectively and mounted on the front of the instructors panel assembly. A rheostat control knob I46, likewise mounted on the front of the panel assembly, serves to control the rate of climb or dive, as the case may be, by permitting the rate of speed at which the drum is turned to be The various indicia or figures IA and TA progress arithmetically as they appear through the window I04 when the drum is rotated in a clockwise direction, and consequently when the drum is thus rotated a climb is in progress. Conversely, when the drum is rotated in the opposit direction a dive is in progress. An altimeter reset switch unit AB is provided in the grouping of control devices I just described and exists for the purpose of restoring the drum to its zero indication at a comparatively rapid rate of speed. A climb indicator I41 and, a dive indicator I49, which are in the form of panel lights, are provided immediately below the climb and dive switches C and D.

True altitude readings and average temperature readings which the bombardier is required to calculate are made available to the instructor automatically. The altitude readings are made available by virtue of the drum position and these readings are taken respectively through the openings I42 and I44 in the drum shutter. Average temperature readings are taken directly from a scale I85 positioned below the opening I04 and having indicia thereon which are identified by their alignment with the particular opening I44 appearing in the window I04. The particular 1 problem at hand, selected by the instructor, is automatically entered into the drum reading by means of a plurality of average temperature correction cams and altitude correction cams disposed in two groups. As will be explained later, since the altitude correction factor ilnvolved is in part dependent upon the free air temperature, the latter altitude correction cams are hereinafter referred to as free air cams. The average temperature cam group is designated in its entirety at I48, while the altitude or free air cam group is designated at 2I4. While any desired number of cams within the limits of mechanical expediency may be employed, for purposes of illustration in the present instance six such cams have been shown in the first group and are designated reading from left to right in Fig. 5 as a, b, c, d, e, and a similar number of cams appear in the second group and are designated reading from left to right at a, b, c, d, e, i. Each of these cams represents a particular problem requiring different calculations on the part of the bombardier due to altitude or temperature variations. Insofar as temperature is concerned, the cams in the group I48 are caused to alter the drum reading or set thereinto a correction factor by the expedient of altering the position of the drum shutter I34 in steps which, because of the fact that there are six cams, may assume at the will of the instructor, any one of six initial starting positions. Toward this end these cams are each provided with circumferential cam surfaces Which are provided with relatively abrupt degrees of eccentricity. The true altitude reading of the drum will, therefore, at any given instant be the combined product of the particular position of the rotating drum and of the particular position of the drum shutter I34. The cams I48 are also designed to eliminate the necessity of the instructor performing the sam calculations that are required of the Ioombardier in making temperature readings at each 1,000 foot level during a climb to determine the corrected altitude. By reading the scale I05 below the window I04 and aligned with one of the openings I44 in the shutter I34, the instructor may tell at a glance the average temperature that would be obtained by taking temperature readings at each one-thousand feet on the bombardiers free air indicator.

The means whereby the position of the shutter I84 may be shifted at will and whereby selection of the various cams a, b, c, d, e or 1 may be made is best illustrated in Figs. 2, 5 and 6. In this last figure only a single cam of the group I48, namely the cam b, is shown. The remaining cam-s of the group have been omitted, while at the same time various parts of the altimeter drum drive assembly have been omitted or broken away to more clearly reveal the nature of the invention. The cam group I48 is mounted on or integrally formed with a sleeve I58 which is slidably keyed as at I5I to a shaft I52 hereinafter referred to as the cam shaft. The previously mentioned element I28 of the drum coupling I26, I28 is mounted on the extreme left-hand end of the cam shaft I52 as viewed in Fig, 6. The coupling element I28 is formed with a pin I54 in its peripheral region and extends into a slot I56 (Fig. 4) formed in the coupling member I26, and thus the drum is adapted to be directly driven from the cam shaft I52. The cam shaft I52 is rotatably carried in a pair of end plates I51 and I59 (Fig. 6) that extend upwardly from a plurality of base members or cross pieces I6I that form a support or base for the altimeter drive unit 14.

The various cams a, b, c, d, e and f are adapted to be shifted laterally along the shaft I52 so as to b selectively moved into register with a cam follower I58 carried at the free end of an arm I60. The arm is secured to and movable with a shaft I82 which for descriptive purposes will hereinafter be referred to as the average temperature shaft. This shaft is pivotally mounted in the end plates I51 and I59 and carries at one end thereof a coupling member I64 similar to the coupling element I28 and which has for its counterpart a member I66 mounted on a shutter rock shaft I68 (Fig. 4), the ends of which are rotatably journaled in the side plates I I4 and I I6 of the altimeter drum unit 12. The shutter sleeves I40 have mounted thereon a pair of gears I10 (Fig. 3) at opposit ends of the drum and these gears have meshing therewith the toothed edges of a pair of segments I12 mounted on the shaft I68.

Referring now to Figs. 5 and 6 wherein the means for shifting the cam group I48 to make selection or the various cams a, b, c, d, e or f is best illustrated, the cam sleeve I50 is formed with a cylindrical groove I13 in a medial region which cooperates with a cam shift fork I14 which projects upwardly from a cam shift rack I16 having a series of gear teeth I18 formed in its underneath side. The teeth I18 are adapted to mesh with an elongated gear I carried at the inner end of a rod I82 which is slidably carried in a U-shaped bracket I84 and which projects through the front wall of the panel unit. A spring I85 surrounds the rod I82 and normally biases the same inwardly of the apparatus to an inoperative position. The outer end of the rod I82 carries a cam shift knob I86.

Still referring to Figs. 5 and 6, a cam shift interlock lever I88 is pivoted medially of its ends on a. pivot studv I90. The lever I88 is provided 1 nnmsi 1 with an upstanding z-rpi'n' I 921' that? projects into a "v groove liltforme'd in a 'collar' I96 mounted onathe l 'rod l82. Thus itwill be'seenzthat shiftinge'move- *ment of the rod 182 byfm'eans of the cam shift -'knob will be accompanied by horizontal-rockingwmovement of the lever 188.; The interlock 'le'vertil88 is provided witha-"downwardlyz turned fiange==i98 through-which thereiprojects a 'cam shift interlock thrust rod' 2El0-"carrying at its outer end a cam .shift interlocka knob- *2 02 end of the thrust rod'r2llfl is formed with athrust pm 2114 designed for engagement with the lower bend of ailift'arm 236 inithe. form of-abellrcrank levermounted on the average-temperatureshaft |62=and the upperend of whichzlever carries a pinflElB which underliesithe upperxend of -an average temperature-Iiftarm'Z I which secured to the average temperature-shaft I62. Aconc-ventionalifdash' pot including a, cylinder I81 secured within theu bracketlfld- 'and-a-having a. piston 189 operatively :con'nected to the extreme right-hand end of 'theinterl'ocklever 488, as ff'ishow'n in Fig. 5;=serves asawcushioningdevice to prevent clashing of: partsz'during: manipulation ofthe" cam'release instrumentalities. -From the above description of parts it will be seenthat :"pushing in on thecam shift interlock knob i 202 'will'ope'rate to rock the average temperature shaft'vl62about its axis and lift the cam follower 158 out of engagement with: that particular cam 'a, b, c, d, Ie or"f%wlith which itais in-register. --"When this is done the cam shift knob 'maybe *rotated so as to cause'the gear I80 to operate on thegeari-teeth' lifl'and shift the cam shift rack H6 in onedire'ction or the-other and thus I bringa selected cam a, b, c, cZ,--e orxf into register :with the camfollower' I581= At thesame time, pushing in on the-cam shiftwinterlockknob 202 will operate through the drum 'shutter'coupling I 16d, I66, to s'wing'thedrumshutter134 about its axis toward a-position of-maximum reading.

T-"Referring now to-Fig. 5;the bracket l84 has formed thereon a s'eries of forwardly-projecting "*pins I 19 which are designed for selective registry with an equal number of holes I81 formed in 1 a locating disc-I83 mounted on'therod I82; The spacing of the'pins E'HSand of the-holes 181i is "such that when registry occurs .therebetween a particular selectedcam in' ithetrgroupn'l48'--will "fall into register With thefollower l58 and simi- 'larly,'a particularselected cam in the-igroup 2l4 will fall into register with a'follow1n232l With the pins and holes in 'registenlthecam' sleeveil50 l willthus be locked in a selected-xposition oft-"adjustment. 1 still referrin'g to Figs/5: and 6, the-previously mentioned series of six' free' airiJ-cams 214' "are formed on th sleeve 150-. and+arewprovidedwfor the dual'purpos'e of controlling-the reading'of the free air temperature meter I00; as-well asforl the purpose of entering a'temperaturezcorrection factor into the calculation for indicatedi airspeed as shown by the'indicator 80. V

The first of these functions is accomplished by means of a potentiometer 216 (se'ealso' Fig; 8)"

which is adjustably mounted in brackets 12 I8 and "220 'afiiXed to'the' end plate I 51 and havingiassoci- "ated therewith a slidingcontact 224' carried at *"the'lower end of an arm 226 that depends from r a rock 'shaft 228here'inafter referredto 'as the 1 free air teinp'erature shaft.

The shaft 228 is supported between the end plates" I 51 and-159 and carries an "arm 230- that projects forwardly to--the vicinity ofNthecam group 2 i l-and isprovided witii'the cam-i follower:

22232 idesignedzfor selective-engagement? with zzthe iiv'arious cams (21", b, c.',- d, e,- and f of the group. :5.- At? thegrearof :the.unit; there ismounted a )sfixed: potentiometer 2|! Fig. 2)- and a---trimmer pctentiometer. 2 I9. Ther-trimmerpotentiometer r .2 I9; fixed potentiometer 2 l 1- and variable potenmtiomete'rilfi area-rranged in an-relectrical cir- 1: lbllit which is in'th'e form of "aWheatstone bridge :r'circuimthat operates to establish the position of 10 .the pointer:associated-with*the free air temperar-iturezindicator: Hi0 asset forth in the above-menationed divisional application. It is tobe? noted fccthat-pushing in on the camshift interlock knob :Z021willoperate through the medium of :the pin 5288 to elevate an arm 234' which is afiixed tovthe lyish'aftvzzfii Such irocking movement of therarm 2234 serves torrock the shaft 228' about its-.aXis and cause-thearmflfl to becomeelevated awayi'from -;:the particular-cam. withrwhich it iswassociated sorzthatshifting of-the 'cam shift rack -fl6cmay be riesorted to.

":i InsFigsG a switch S is shown as beingmounted immediately rearW-ardly of theica-m' shift interlock leverwl88; This switch is'radapted to -be engaged bygthis-latter lever::when therinterlock knob 202 3 is zpushed inwardly" to-open-:zthe.circuit: to the :driving motor M.

-:;The:second of the above :men-tioned functions Of"' the1"SiX fi'e8 air-"cams in the group 2I4 is oraccommodated through the medium ofan; air- :2 speed correctionzunitxdesignated in its entirety at 233 Fig. and is drivenduringclimb or dive y operations and consequently-during movement l of the altimeter drum; .1 06. Therdr-iving-connection-for direct driving of the airspeed-correction 1. unit1238 from the motor M-duringfclimb anddive qfioperat-ions; as, well as thesconnectionstherefor z-wherebythe-fre s air temperature correction factorzinvolved isentered intothe airspeed indicator 40 8'2, will beset "forth indetail after adescription 1: has'been given of the ;drivingconnection existing .erbetween-the-motor and-the; altimeter drum 406. I :-1The driving connectionjust referred to includes a :agear redu'ctionunit MD-Fig. 7 .WhOSB'iillD'I-li} is a ;motor shaftq2t2 fth'emotor Maand-which at. its 1 .output-sideserves.througbazpair of bevel gears 24 land 263 to drivea:gear'reductionv train: desig- =--nated in: its entirety: at-2M-leading to adriving a gear-246 mounted on one .end ofthe cam shaft l 52 5oand-which is: directly-coupled to the-drumai flfi-iby :means of":the':coup1-in'g- [26, 1 |28.1;=The;;gean 246 T. meshes with an" altitude correction aentryag ear :1. 256 which constitutesronednputgear associated :with 4 the air spe'ed correction .unit -2 38.

55 The airspeedrcorre'ction unit-523.8 is in -the ;form of a. removable assemblyco-mplet-e in itself; n'I-his assembly forms: no part of :the present invention -Iand isincluded as-ypart of the subject matter of f the above-mentioned divisional application.

Th airspee'd"-.correction :unit: 238 includes a 'casingU-ZSZ' (Fig.- 2')-:which iissecured in position a 1 fbetween'the two end-plates :I 515159:- :-The'-mechanism-includes amultiple differential 'gear system :1: which receives its initial .drive from a; gear: .256

shown :betweerrthe drum.unit 1:2 and"v the drive unit" M in Fig. :2rand hereinafter-referred to as thef'trueairspeed entrygear. v This latter gear -is-adapted to be manually driven by the instructor 1 by" means of": airspeed" 'jcrank *2 58" :(Fig; 1 1) 7 ocatedat -the-instructorsr seteuppainel 4G-and serves to set a-reading ofztrue airspeedinto'zthe a trueairspeedindicator 80. Thefdrivingponnecwr'tion :just referred to .le'adsrfrom the-;fcrank-:258

;-ithrough .aipulleyvand cable: system 262 toa-zdrum 9 the panel unit and which is shown at the lefthand side of Figs. 2 and 7.

The pulley 264 is mounted on one end of a shaft 265 (see Figs. 2, 5, 6 and 7) and which has mounted on its other end a gear 268 (Fig. 6) hereinafter referred to as the true airspeed drive gear. The gear 268 meshes with a gear 210 loosely mounted on the shaft 152 behind the coupling member I28 (Fig. 6) which in turn meshes with the true airspeed entry gear 256.

In actual practice, using standard instruments, the computing means for calculating true airspeed from indicated airspeed is based upon a logarithmic scale, the reading in knots obtained on the dial of the true airspeed indicator 80 as well as on the dial of the indicated airspeed instrument B2 are expressed by graduations that are spaced logarithmically. Thus, the airspeed correction unit 238 is provided with a logarithmic correction mechanism for changing the linear factor introduced by the entry gear 256 into a logarithmic factor and introducing the same into the true airspeed indicator 8!]. This mechanism forms the subject matter of the above mentioned divisional application and no detailed description or illustration thereof is made herein,

It is suflicient for the purpose of the present disclosure to state that the airspeed correction unit 238 receives an input from gears 259 and 256 in order to properly operate according to a logarithmic scale the true airspeed indicator 80 and the indicated airspeed instrument 82. In addition, and as previously stated, the reading of the instrument 82, in addition to being a function of the true airspeed, is also a function of the free air temperature and of the altitude at the instant of reading. Temperature correction is entered under the influence of the cam group 2 l4 including the cams a, b, c, d, e, and ,1" into the instrument 82 by mean-s of a segment 334 mounted on the fre air temperature shaft 228. This segment is adapted upon rocking movement of the shaft 228 under th influence of any one of the selected free air cams in the group 2, to impart movement to a gear 336 (Fig. 2) included in the multiple differential gear system of the airspeed correction unit 238. Thus this latter gear 336 constitutes a further input for the unit 238, the details of which have been set forth in the above mentioned divisional application.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the apparatus illustrated and in its 10 operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claim,

What is claimed is:

In an apparatus of the character described, a rotary cam shaft, a sleeve slidably splined to said shaft, a cam cluster mounted on said sleeve and including a plurality of cam elements arranged in spaced relationship, a cam follower mounted for movement in a vertical plane and designed for selective engagement with said cams, means normally maintaining said follower in engagement with a selected cam, and selecting means for shifting said sleeve longitudinally of the shaft on which it is mounted comprising a cam shift rack mounted for sliding movement longitudinally of the shaft, ther being a groove formed in said sleeve, a cam shift fork carried by said rack, there being a series of teeth formed on said rack, a gear cooperating with said rack and movable transversely of said shaft, an operating rod secured to said gear, locating means for said operating rod whereby th latter may assume a number of angular positions corresponding to the number of cams on said sleeve and whereby in any selected angular position of the rod 2. selected cam will be in register with said follower, said rod being movable from a retracted position wherein said locating means is inoperative to prevent turning of the rod to an advanced position wherein said rod is locked against turning movement, and means for elevating said follower out of the path of movement of said cams upon movement of said operating rod to its retracted position.

GEORGE F. DALY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,536,119 McDonald May 5, 1925 1,720,189 Jackson July 9, 1929 1,893,882 Burke Jan. 10, 1933 1,939,706 Karnes Dec. 19, 1933 2,023,488 Poppen Dec. 10, 1935 2,110,869 Crane Mar. 15, 1938 2,164,412 Koster July 4, 1939 2,321,799 Cone June 15, 1943 2,359,059 Somes Sept. 26, 1944 2,364,539 Link Dec. 5, 1944 2,376,572 Burdick May 22, 1945 

